Purpose of this Research Plan is the non-invasive identification and grading of atherosclerotic lesions (stenosis and occlusions) by non-invasive methods: indirect arterial pressure recording (Doppler), and waveform analysis of the velocity tracing obtained by Doppler ultrasound, before and after exercise. Bruits caused by a stenotic lesion are also recorded and their spectral content is determined to evaluate the hemodynamic significance of lesions. Experiments are being done at three levels: (a) in arterial circulatory (physical) models and (b) in dogs with stenoses of known geometry and vessels with known flow rates, (c) determinations are also being made in normal subjects and in patients with atherosclerosis. Data obtained from patients are stored on computer files. Hypotheses validated in bench and animal experiments will be used for correlation of patient's measurements with their angiographic and clinical data.